Hydrogen can be produced in a hybrid sulfur cycle that utilizes an electrolyzer cell that has both an anode and a cathode. The hybrid sulfur cycle is a hybrid thermochemical cycle that can be used in conjunction with advanced nuclear reactors or centralized solar receivers to produce hydrogen by water splitting. The hybrid sulfur cycle uses high temperature, usually greater than 800° Celsius, thermal decomposition of sulfuric acid to produce oxygen and regenerate sulfur dioxide. The hybrid sulfur cycle is capable of generating hydrogen in a water electrolyzer at voltages lower than other methods such as conventional water electrolysis.
Sulfur dioxide and deionized water may be used as the anode reactants and can react at the anode to form sulfuric acid and protons (H+). The anode reaction may be: SO2 (aq)+2H2O (aq)⇄H2SO4 (aq)+2H+ (aq)+2e−. The electrolyzer cell includes a membrane that allows the hydrogen ions produced at the anode to pass through. The membrane may allow the hydrogen ions to pass while preventing hydrogen gas, sulfuric acid, or other chemical species from passing through. The hydrogen ions can be used at the cathode reaction that may be 2H+ (aq)+2e−→H2 (g). The hydrogen gas generated at the cathode can then be collected as desired. Water is generally introduced at the cathode to maintain hydration of this component. The hybrid sulfur cycle is capable of generating hydrogen at a much lower voltage than conventional electrolysis
Although capable of producing hydrogen gas, without the disclosed methodology the use of an electrolyzer cell most likely requires a greater amount of voltage over time to drive the reaction. This increase in voltage is due to the formation of a sulfur layer between the cathode and the membrane. The presence of the sulfur layer adds ohmic resistance to the membrane electrode assembly, which increases cell voltage, and also presses the membrane electrode assembly into anode flow passages that increase pressure drop. Aside from increasing the voltage necessary to drive the production of hydrogen, the presence of the sulfur layer acts to delaminate the membrane electrode assembly and reduce the operational life of the apparatus. Hydrogen may be potentially used to replace gasoline as a transportation fuel and thus it may be necessary to generate millions of tons of hydrogen per year. Accordingly, there remains room for variation and improvement within the art.